1. Field of Invention
The present invention relates to an improved side bearing design for mounting on a railroad car truck bolster that allows long travel, substantial weight reduction, improved hunting and curving characteristics, and various safety features.
2. Description of Related Art
In a typical railway freight train, such as that shown in FIG. 1, railway cars 12, 14 are connected end to end by couplers 16, 18. Couplers 16, 18 are each received in draft sills 20, 22 of each respective car along with hydraulic cushioning or other shock-absorbing assemblies (unshown). Draft sills 20, 22 are provided at the ends of the railway car's center sill, and include center plates that rest in center plate bowls of railway car trucks 26, 28.
As better shown in FIG. 2, each typical car truck 26 includes a pair of side frames 30, 32 supported on wheel sets 34, 36. A hollow bolster 38 extends between and is supported on springs 40 mounted on the side frames. A bolster center plate 24 is provided having a central opening 42. The bolster center plate bowl 24 receives and supports a circular center plate of the draft sill 20. Side bearing pads 60 are provided laterally to each side of center plate 24 on bolster 38. Side frames 30, 32 comprise a top member 44, compression member 46, tension member 48, column 50, gib 52, pedestal 54, pedestal roof 56, bearing 58 and bearing adapter 62.
Constant contact side bearings are commonly used on railroad car trucks. They are typically located on the truck bolster, such as on side bearing pads 60, but may be located elsewhere. Some prior designs have used a single helical spring mounted between a base and a cap. Others use multiple helical springs or elastomer elements. Exemplary known side bearing arrangements include U.S. Pat. No. 3,748,001 to Neumann et al. and U.S. Pat. No. 4,130,066 to Mulcahy, the substance of which are incorporated herein by reference in their entirety.
Typical side bearing arrangements are designed to control hunting of the railroad car. That is, as the semi-conical wheels of the railcar truck ride along a railroad track, a yaw axis motion is induced in the railroad car truck. As the truck yaws, part of the side bearing is made to slide across the underside the wear plate bolted to the railroad car body bolster. The resulting friction produces an opposing torque that acts to prevent this yaw motion. Another purpose of railroad car truck side bearings is to control or limit the roll motion of the car body. Most prior side bearing designs limited travel of the bearings to about 5/16″. The maximum travel of such side bearings is specified by the Association of American Railroads (AAR) standards. Previous standards, such as M-948-77, limited travel to 5/16″ for many applications.
New standards have evolved requiring side bearings that have improved hunting, curving and other properties to further increase the safety and design of railcars. The most recent AAR standard is M-976 that now allows for long travel side bearings and has several new requirements, such as new specifications for bearing preloads. Preload is defined as the force applied by the spring element when the Constant Contact Side Bearing is set at the prescribed height.